The present invention disclosed herein relates to a photosensitive drum driving assembly for receiving a driving force provided from a main body of an image forming apparatus, a photosensitive drum assembly, a process cartridge, and the image forming apparatus, and more particularly, to a photosensitive drum driving assembly and a photosensitive drum assembly, a process cartridge, and an image forming apparatus, which can rotate a photosensitive drum while minimizing a loss of a driving force provided from a main body of an image forming apparatus and can ensure a reliable and longer lifespan.
Generally, examples of image forming apparatuses, which print characters or images on recording materials such as paper, include copy machines, laser printers, LED printers, and facsimiles.
An image forming apparatus includes a toner and a cartridge that records characters and images on recording materials such as paper. The cartridge is detachably provided for replacement of the toner.
FIG. 1 is a schematic view illustrating the configuration of a typical image forming apparatus. FIG. 2 is a perspective view illustrating the exterior of a cartridge of FIG. 1. FIG. 3 is a cross-sectional view illustrating a photosensitive drum of the cartridge of FIG. 1 and a peripheral configuration thereof.
Referring to FIGS. 1 through 3, the image forming apparatus includes a process cartridge that stores a toner and supplies the toner to a recording material. The image forming apparatus feeds the recording material 88 such as paper in a direction 88s while rotating a plurality of rollers 73, 74, 75, 76 and 77 disposed in a main body 1. Simultaneously, the image forming apparatus delivers data such as images to the process cartridge 2, and transcribes the toner stored in a toner storage 28 on the recording material as necessary through a photosensitive drum 10 to print a desired image on the recording material 88.
For this, the process cartridge 2 includes a photosensitive drum 10, a cleaning unit, a writing unit, and a developing unit. Electric charges that reach the photosensitive drum 10 cause photosensitivity. After the toner is electrodeposited on a sensitized portion, the toner is moved onto a paper, and then heat is applied to fix an image on the paper.
The process cartridge 2 is provided detachably from the main body 1. When the process cartridge is mounted, a driving assembly 20 coupled to the photosensitive drum 10 is coupled to a driving force providing apparatus provided in the main body 1 to receive a rotary driving force. Specifically, a protrusion 21p for receiving a rotary force is protrusively formed at the end portion of the driving assembly to be coupled to components provided in the main body 1.
The reference numeral 49 unexplained denotes a case for supporting the rotation of the photosensitive drum 10 of the process cartridge 2, and the reference numeral 30g unexplained denotes a gear that is disposed at a side opposite to the driving assembly 20 and transfers a rotary force. Also, the reference numeral 29 unexplained denotes a support that is protrusively formed on the driving assembly 20, and the reference numeral 23g unexplained denotes a gear that is disposed on the outer circumferential surface of the driving assembly 20.
FIGS. 4 and 5 are perspective views illustrating a rotation driving force transmission structure of a typical image forming apparatus. Specifically, FIGS. 4 and 5 illustrate a rotary driving force transmission structure of an image forming apparatus disclosed in Korean Patent No. 258609, which transfers a driving force by the method described above.
Referring to FIGS. 4 and 5, when a process cartridge 2 is inserted into a main body of an image forming apparatus, a twisted protrusion 21p of a driving assembly 20 coupled to one side of a photosensitive drum 10 provided in the process cartridge 2 is inserted into a twisted hole 181 of a drive shaft 180 provided in the main body 1. As the drive shaft 180 is rotated by a driving motor provided in the main body 1 of the image forming apparatus, the twisted hole 181 of the drive shaft 180 and the twisted protrusion 210 are coupled to each other to be rotated. Thus, a driving force provided from the driving motor is transferred to the photosensitive drum 10 to allow the photosensitive drum 10 to rotate.
In this case, the twisted protrusion 21p is in point contact with the inner surface of the twisted hole 181 at three portions when viewing the section of the twisted protrusion 21p. As a whole, a driving force is transferred through line contact at the three portions.
The drive shaft 180 includes a gear part 182g for receiving a driving force from the driving motor.
However, there is the following limitation in the typical technology described above.
Since a driving force is transferred by a point contact based on the section, a stress is concentrated on a small contact point, increasing the abrasion speed. Accordingly, the contact point is easily abraded or damaged, making it difficult to achieve exact performance during the expected lifespan. Specifically, regarding the characteristics of Korean Patent No. 258609, the twisted protrusion 21p contacts the inner surface of the twisted hole 181 when a driving force is being transferred, and is spaced from the inner surface of the twisted hole 181 when a driving force is not being transferred. Thus, the point contact portion, i.e., the angular point portion of the twisted protrusion 21p is inevitably and continuously exposed to a certain level of repeated shock and friction. Particularly, since printing is performed several thousand times until the cartridge is replaced, loads such as shock or friction applied to the twisted protrusion 21p may reach a considerable level. Due to such repetitive load, the point contact portion of the twisted protrusion 21p may be easily abraded or damaged. Furthermore, when the twisted protrusion 21p rotates while being inserted into the twisted hole 181, the twisted protrusion 21p becomes in point contact with the twisted hole 181. Accordingly, it is unstable for the twisted protrusion 21p to be seated on a location where the rotary driving force is exactly transferred.
When the point contact portion of the twisted protrusion 21p is abraded or damaged, the rotation precision is reduced upon rotation of the photosensitive drum, making it difficult to maintaining the concentricity of the drive shaft 180 and the photosensitive drum 10. In other words, the photosensitive drum 10 may vibrate during its rotation, and may affect the image quality of the image forming apparatus 1.